Electrical musical instrument with frequency divider circuit



H. BODE Sept. 29, 1959 ELECTRICAL MUSICAL INSTRUMENT WITH FREQUENCYDIVIDER CIRCUIT Filed July 6, 1954 2 Sheets-Sheet l [FIG Lu 3.1., 1mm

Sept. 29, 1959 H. BODE 06,960

ELECTRICAL MUSICAL INSTRUMENT WITH FREQUENCY DIVIDER CIRCUIT Filed July6, 1954 2 Sheets-Sheet 2 KEY SWITCHES KEY SWITCHES United States PatentOfiice Patented Sept. 29, 1959 ELECTRICAL MUSICAL INSTRUMENT WITHFREQUENCY DIVIDER CIRCUIT Harald Bode, Brattleboro, Vt., assignor, bymsne assignments, to Estey Organ Corporation (Del.), New York, N.Y., acorporation of Delaware Application July 6, 1954, Serial No. 441,254Claims priority, application Germany September 5, 1953 1 Claim. (Cl.331- 51) This invention relates to electronic musical instruments andmore particularly it relates to a frequency divider adapted to generatetones in an electronic musical instrument.

It is an object of the present invention to provide a type of frequencydivider which lends itself to use in an electronic organ of relativelysmall, light, handy and, compact construction.

It is a further object of the invention to provide a miniature organ orsimilar musical instrument which may be housed in a portable carryingcase containing in addition to the electronic circuitry necessary toproduce the musical tones, the amplifier and speaker associated with theorgan.

In order to provide an electronic musical instrument of theabove-mentioned character, one of the most important considerations isthe type of electronic tone generators to be employed owing to the factsuch a larger number of these generators are necessary. Naturally,besides the requirement that the generators occupy a minimum of spaceand do not require an excess of power, it is also most important thatthey have relatively high frequency stability. To these ends, tonegenerators in the form of frequency dividers, synchronized in the firstinstance by a master oscillator, have proven effective, particularlythose frequency divider circuits which employ only resistors andcapacitors by virtue of the saving in space and weight which theyafford. One example of such a frequency divider circuit which has beenused in the past is the socalled reactance tube circuit, which is tunedby means of fixed capacitors. However, a basic failing of the reactancetube circuit in a frequency divider application is the inability of thelower divider stages to oscillate reliably. In fact, they are likely tocut oif completely as the characteristics of the electronic tubesemployed therein and the associated components change with age makingthem ill-suited for use in a musical instrument.

According to the invention, therefore, there is provided a frequencydivider which embodies a phase shift oscib lator having a feed-backnetwork or phase shifting net work of the ladder type with a capactiveelement in each series arm and a resistive element in each shunt arm. Inorder'to couple the network to the input or control circult of theoscillator there is provided in the last shunt arm, a voltage dividingarrangement so that the signals representing tones, generated by thefrequency divider, will not be reflected in the output precedingfrequency divider stage or in the master oscillator stage coupledthereto for synchronization purposes.

The novel feature of the invention, together with further objects andadvantages thereof, will become more readily apparent when considered inconnection with the accompanying drawings in which:

Fig. l is a schematic diagram of a chain of two frequency divider stagesaccording to the invention;

Fig. 2 is a schematic diagram of a single frequency divider stage incombination with a master oscillator stage in accordance with theinvention;

Fig. 3 is a perspective view illustrating a preferred mountingarrangement for a master oscillator and frequency divider chainaccording to the invention;

Fig. 4 is a sectional view taken on line 4, 4 of Fig. 3;

Fig. 5 is perspective view showing a modification of the mountingarrangement of Fig. 4;

Fig. 6 is a side view in elevation of a portable organ case adapted tohouse a plurality of the sub-assemblies of Fig. 3; and

Fig. 7 is a view in elevation of a modification of the assemblyaccording to Fig. 5.

Referring now to the drawings, and more particularly to Fig. 1, it willbe observed that a chain of two frequency divider stages according tothe invention have been illustrated schematically, the first one in thechain being adapted to synchronize the second, and the first one itselfbeing synchronized by either another frequency divider stage or a masteroscillator stage (not shown), having its output circuit coupled betweenan input terminal 30 and ground as represented by terminal 0. The firstfrequency divider stage in the diagram of Fig. 1 includes a triodeelectron discharge device 1 having an anode circuit or output circuitcoupled between a source of anode potential, as represented by terminalB+, and ground; and having a control circuit or input circuit which iscoupled to the output circuit in order to induce oscillation. To thisend, there is provided a feedback or phase shifting network coupled tothe output circuit, or more particularly coupled between the anode endof an anode resistor 12 and ground, and having a substantially phaseshifting characteristic at the desired operating frequency of thisstage. As shown in Fig. 1, network 16 is of the ladder type and includescapacitors 2, 3, 4, and 5, respectively, in each series arm, andresistors 6, 7 and 8, respectively, in each shunt arm. The last shuntarm is formed with a pair of resistors 9 and 10 which serve as a voltagedividing arrangement so that only a portion of the signal voltagetransmitted by the network will be impressed on the master generator.That is to say, the control electrode or grid of triode 1 is connectedto the junction of resistor 9 and capacitor 5 and the cathode of thetriode as well as the end of resistor 10 remote from this junction areconnected to ground. To synchronize the frequency divider stage,terminal 30 is connected to the junction of resistors 9 and 10 through acapacitor 11.

With reference to the second frequency divider stage of Fig. 1, it willbe observed that the same employs a triode electron discharge device 15in an arrangement like that of triode 1 of the first frequency dividerstage. The phase shifting network in the case of'the second frequencydivider stage has been designated generally by the number 17 and tosynchronize the second frequency divider stage at a subharmonicordinarily the first sub harmonic of the tone signals generated by thefirst stage, there is provided a coupling capacitor 14 connected betweenthe anode of triode 1 and the junction of resistors 9' and 10' whichfunction in the same manner as do resistors 9 and 10 discussedhereinabove.

As will be apparent to those skilled in the art, the number of armsemployed in each of the phase shifting networks 16 and 17 is notnecessarily limited to 4 just so long as the output tone signalsdeveloped in the anode circuits of each triode 1 and 15 are transmittedto the respective control circuits thereof with a phase shift ofsubstantially 180 at the desired frequency of operation. As is wellknown, under such circumstances, the condition for oscillation will besatisfied, and owing to the synchronizing signals applied to therespective control circuits of the triodes, the frequency of theoscillations will be locked in at a different subharmonic, in each case,of the master oscillator frequency. It is preferred that four or moreseries and shunt arms be employed in the phase shift network, however,since the tolerances of .the resistors and capacitorstwhich form thearms need is a Hartley oscillator because of the small inductor which itemploys relative to its frequency of operation, namely the frequency ofone of the tones in the highest octave. Another example of a masteroscillator which is particularly well adapted for use with one or morefrequency dividers according to the invention is shown in Fig. 2. w 7

Referring now to Fig. 2, those skilled in the art will recognize thattriodes 18- and 19 and their associated circuitry comprise a Wien bridgeoscillator. Since the oscillator is well known, and forms no part of thepresent invention, it will not be described in detail. One methodof'producing vibrato in such an oscillator is to apply to its controlcircuit, that is to the control circuit of triode 13, an alternatingvoltage whose frequency corresponds to the rhythm of the particularvibrato desired. This will produce in the output signal of theoscillator a small amount of frequency modulation which in turn will bereflected in the output signals from the respective frequency dividerstages. In a complete instrument, ordinarily l2 master oscillators arenecessary to generate the 12 semitones of the highest octave and hencethe control circuits of the various triodes which function as doestriode 18 may be interconnected so that only a single vibrato powersupply need be employed. In this event capacitor 27, which is connectedacross the control circuit of triode 18 in Fig. 2, prevents cross talkbetween the respective master oscillators It is pro-posed, as shown inFigs. 3 and 4 that the various electron discharge devices, or tubes,employed in the frequency dividers according to the invention be mountedon a U-shaped channel member 28 of metal, and that a panel 29 ofinsulating material be fastened to one of the shanks of the U as shown.Soldering lugs V in the form of eyelets are then fastened to the panel29 for providing input and output connections to the frequency dividerand oscillator circuitry, although it will be understood that variousother forms of connectors are equally suitable. Fig. 5. illustrates amounting arrangement like that of Figs. 3 and 4 except that panel 29extends above member 28 rather than 'belowit;

In a completemusical instrument. wherein l2 master oscillators and 12frequency divider chains are employed, it is proposed that each of theunits or sub-assemblies as shown in Fig. 3 be arranged in a Z-shapedhousing or case as shown in Fig, 6. Fig. 7 illustrates a similararrangement of the-sub-assemblies of'Fig. 5;

Various other modifications within the spirit and scope of theinvention, particularly as regards the frequency divider itself, willoccurto those skilled in the art so that the invention should be deemedto be limited only by the scope of the appended claim. What is claimedIn combination with a master tone generator for an electronic musicalinstrument, at least one frequency divider to provide subharmonicallyrelated tones, said frequency divider comprising an'electron dischargedevice having a control circuit and an anode circuit and, a ladder typefeedback network connected between said control circuit and said anodecircuit, said feedback network having a capacitive element in eachseries arm and a resistive element in each shunt arm, and the last ofsaid shunt. arms being formed with a pair of series connected resistiveelements, one of which is connected. to said master generator to causesaid frequency divider to oscillate in synchronism with said mastergenerator without disturbing appreciably the tones generated by thelatter.

ReferencesCited in the file of this patent UNITED STATES PATENTSMontgomery Feb. 2, 1954 OTHER REFERENCES Article: Frequency Divisionwith Phase-Shift Oscillators by Schmidt, pp( 111-113ofElectronicsforlune 1950.

